The present invention relates generally to automotive friction clutches, and more particularly to clutch cover assemblies which comprise a unitary assembly which is mounted on a reaction plate or flywheel after the insertion of a friction plate or driven disc therebetween to make up the clutch.
Generally speaking, such a clutch cover assembly comprises a plurality of generally annular members including a cover, a pressure plate connected for rotation with the cover by attachment means permitting limited axial displacement of the pressure plate relative to the cover. The cover assembly further comprises between the cover and the pressure plate axially acting resilient means bearing against the cover and applied against the pressure plate to urge the pressure plate axially away from the cover.
The present invention relates more particularly to the case where between the cover and the pressure plate are provided abutment means for axially retaining the pressure plate after predetermined axial travel relative to the cover. Indeed, it has been established that in at least certain applications it is desirable to limit the axial travel of the pressure plate against the axially acting resilient means. This is especially true when the attachment means attaching the pressure plate to the cover not only have the function of transmitting torque between the cover and the pressure plate while permitting axial displacement of the pressure plate relative to the cover, but also when they ensure the function of resiliently urging the pressure plate away from the associated clutch plate for clutch disengagement.
As is known the attachment means are usually formed by spring steel straps which are disposed generally transversely relative to the axis of the assembly or generally radially, and have a rather low axial stiffness.
Moreover, when cover assembly is unloaded, i.e., before mounting on the reaction plate or when handling the cover assembly on its own, the straps may be deformed to the detriment to their service life and/or effectiveness if measures are not taken to limit the axial displacement of the pressure plate relative to the cover under the action of the axially acting resilient means on the pressure plate, the latter not being in axial abutment.
In practice, when the axially acting resilient means comprise a diaphragm spring having a Belleville washer peripheral portion and a central portion divided into radial fingers for controlling the release of the peripheral portion, it is usual to provide along the inner periphery of the cover radial tabs. The radial fingers of the diaphragm spring come to bear against the inner periphery of the tabs on the cover which limits the resilient force applied to the pressure plate by the diaphragm and therefore the axial displacement of the pressure plate relative to the cover.
Yet, but in this situation, in the course of a handling the cover assembly without any particular precautions in its unloaded condition, owing to its substantial weight the pressure plate may be caused to swing sufficiently from the cover to cause a latent defect or damage to the straps attaching the pressure plate to the cover.
Consequently, it is common to provide with the pressure plate abutment means to ensure positive axial retention of the pressure plate to prevent axial displacement beyond a predetermined distance from the cover.
In French patent application No. 2,437,525, the retaining means provided for this purpose comprise retaining lugs formed from the cover, and a transverse shoulder on the pressure plate is adapted to abutment against each retaining lug. In this French patent publication for cooperation with the transverse shoulder formed by the outer surface of the pressure plate directed outwardly relative to the lateral wall of the cover, the retaining lugs extend circumferentially. Each of the retaining lugs is formed by a strike or cutout in the lateral part of the notches usually provided in such a cover for radial lugs on the pressure plate required for fixing to the pressure plate the straps connecting it to the cover.
The circumferentially extension of these retaining lugs has various drawbacks. First of all, there is necessarily a predetermined single direction of rotation depending on the direction of the extension of the retaining lugs whereby the cover assembly can only be used for a single direction of rotation. This direction of rotation corresponds to the straps operating in traction. For cover assemblies having a given direction of rotation covers must be used with retaining lugs extending circumferentially in the corresponding direction.
Further, the cutouts in the lateral part of the notches in the cover for the formation of the retaining lugs necessarily substantially locally weakens the cover.
Finally, the presence of such circumferential retaining lugs makes it is difficult to effect axial abutment in both directions of the pressure plate in order to protect the bending of the straps attaching the pressure plate to the cover, and/or circumferential abutment of the pressure plate to avoid straps buckling.
In DOS No. 2,906,863, the retaining lugs are formed from the cover for cooperation with the radially extending transverse shoulder on the pressure plate, but the pressure plate has on its inner periphery a transverse shoulder which at least in this embodiment is in continuity with a slot in the pressure plate.
There is a resulting relatively large radial distance between the circumference of the pressure plate on which the retaining lugs are disposed and the circumference of the pressure plate corresponding to the position at which the axially acting resilient means bear. The consequent lack of alignment makes the operation of the retaining lugs rather uncertain.